Traditional spot welding guns are usually custom manufactured for their intended application. These custom weld guns include welding arms that are moved by some type of actuator, such as a pneumatic or servo actuator. The welding arms, yokes, and pivots are often custom configured and may be part of a custom casting including the arms, yokes, pivot supports, and actuator arms. Obviously, custom casting portions of the weld gun raises the cost and complexity of the gun and increases the lead time required for providing the gun for a specific application. In light of this, there is a need for a modular approach to the design and construction of spot welding guns.